Keypads comprising a plurality of different keys usually use encoding methods in order to reduce the number of required electric connections. One common method to encode keys of a keypad is to use two-dimensional encoding combined with a scan process. For this purpose the keys are arranged in a matrix having columns assigned to respective electrical column lines and rows assigned to respective electrical row lines. Such a conventional keypad structure is illustrated in FIG. 1. Each key 2 is coupled to one column line C1-C5 and one row line R1-R5 such that when a key is pressed it connects electrically the column line C1-C5 and the row line R1-R5 at the intersection where the key is located. In order to determine what key has been pressed, or in other words to read the keystrokes, the column lines and the row lines have to be scanned. Scanning can be done, for example, by applying a specific voltage to the column lines one by one and by determining at which row line this voltage can be detected.
In order to apply a voltage to a connection line C1-C5, R1-R5 of the keypad or to read the voltage from such a line the respective line has to be connected to an electronic circuit which then is susceptible to electrostatic discharge.
Further multidimensional encoding of keys of a keypad is known. In multidimensional encoding schemes the keys are coupled to three lines which are connected electrically to each other when the key is pressed. Each of the lines coupled to a key belongs to one of in total three groups of lines. In order to read the keystrokes of this multidimensionally encoded keypad the lines of the three groups of lines have to be scanned accordingly.